**1. Introduction**

250 Biogas

Zhu, H.;. Fang, HP.; Zhang, T.;. Beaudette, LA. (2007). Effect of ferrous ion on photo

*Energy*, vol.32, pp.4112-4118.

heterotrophic hydrogen production by *Rhodobacter sphaeroides*, *Int J Hydrogen* 

Constantly increasing demand for energy has created extensive consumption of fossil fuels and the thread of their exhaustion has became a serious concern. At the same time it has been an inspiration for search for new, environmental friendly energy sources, out of which hydrogen seems to be one of the most promising. It is easily accessible, harmless, renewable and effective (high heat of combustion) energy carrier (Ball, 2009). Within the numerous methods of hydrogen production, biological methods (so called "green technology") have gained substantial importance. These methods consist of fermentative decomposition of organic substances, biophotolysis of water by algae and cyanobacteria, decomposition of organic compounds by photosynthetic bacteria and two-stage hybrid systems with fermentative and photosynthetic bacteria (Waligórska, 2006, Koku, 2002, Su, 2009).

Photofermentation represents the process where heterotrophic bacteria in the presence of light decompose organic substances and produce hydrogen and CO2. It has been already shown that purple non-sulphur bacteria *Rhodobacter sphaeroides* act as efficient biocatalyst in the process of hydrogen production from the wastes coming from breweries and dairy industry. Brewery wastes carry high concentration of organic compounds (COD 0.8- 2.5kg/hl of beer) and represent high volumes (1.3-1.8 hl/hl of beer). The amount of waste during beer production is enormous and equals the amount of water applied for production diminished with water present in beer (usually 3-4 hl of waste per 1 hl of beer). A chemical composition of waste strongly depends on the kind of beer produced and fermentation degree. Such waste can contain aminoacids, proteins, organic acids, sugers, alcohols, as well as vitamins of the B group. (Wojnowska-Baryła, 2002, Srikanth, 2009, Cui, 2009) As far as dairy wastes are concerned, they contain an average of 5-50 g O2 /l. These wastes are mainly composed of remaining of milk, fats and whey. Typical Polish dairy produces 450-600 m3 of wastes per day, half of which goes directly to rivers, lakes and to the ground. These wastes easily undergo fermentation, which causes acidification, intense oxygen consumption, bottom sedimentation and growth of fungi. The organics in both dairy and brewery wastes represent the efficient substrate for *Rhodobacter sphaeroides* and seem to be a promising source for energy production. The efficient use of food wastes in hydrogen generation with

Photofermentative Hydrogen Generation in Presence of Waste Water from Food Industry 253

deionized water and dried at 80oC for 4 h. Elemental analysis of the foot wastes (C,H,N,O) was performed in triplicate using an elemental analyser (Vario EL III Elementary). Concentration of Fe, Ca, Mg in purified wastes was measured by ICP OES spectroscopy. The value of pH was measured with glass electrode ERH-11. The intensity of luminance was measured at the external wall of the bottle with a luxometer Lx204 made by Slandi, Poland and a pyranometer CMP3 by Kipp & Zonen (Waligórska, 2006). The light conversion

( ) *tAI*

where "V" is the volume of produced H2 in liters, "ρ" is the density of the produced hydrogen gas in g/l, "I" is the light intensity in W/m2, "A" is the irradiated area in m2 and

Substrate efficiency Ysub (l /l waste) was calculated as final hydrogen concentration per l of

where Hmax is a final hydrogen concentration in l, Vwaste is waste concentration in l. Specific efficiency Ysp (l H2 /g COD) was calculated based on following equation:

*Y*

hydrogen and carbon dioxide (Mu, 2007, Nath, 2008, Chen, 2006):

max

(h), λ – lag time (h), e – exp = 2.718.

**3. Results and discussion 3.1 Pretreatment of wastes** 

61.33 %

⋅⋅ ⋅⋅ <sup>=</sup> ρ

max *H Ysub Vwaste*

> max *H*

> > ( ) max, <sup>2</sup>

λ

max exp exp 1

*H*

= − − +

where: H - cumulative hydrogen (l/lmedium), Hmax – maximum cumulative hydrogen (l/lmedium), Rmax, H2 –maximum rate of hydrogen production (l/l/h), t – fermentation time

The wastes applied in this series of experiments required high temperature pretreatment (120oC for 20 min), which had significantly increased the efficiency of hydrogen production by removing from the crude waste microorganisms realizing competitive fermentation. The crude wastes were acidic (dairy waste pH 4.2, brewery waste pH 4.7) and contained high concentration of NH4+ (40 mg/l dairy waste and 96 mg/l brewery waste), which can significantly reduce hydrogen production (Waligórska, 2009). High concentration of

*sp CODloss*

The modified Gompertz (Eq. 4) was applied for calculations of cumulative amounts of

*R e <sup>H</sup> H H <sup>t</sup>*

*V*

(1)

= (2)

= (3)

(4)

efficiency (η) was calculated based on the following formula (Koku, 2002):

η

"t" is the duration of hydrogen production in hours.

waste:

simultaneous degradation of these laborious wastes seems to be a very environmentally friendly solution. The US Department of Energy Hydrogen Program in United States estimates that contribution of hydrogen to total energy market will be 8-10% by 2025 (National Hydrogen Energy Roapmap, 2002). It is predicted that hydrogen will become the main carrier of energy in the near future due to environmental and universal applications reasons. It is clean, highly energetic energy carrier (142.35 kJ/g), with almost tripled gravimetric energy density compared to ordinary hydrocarbons. Although the described method is relatively simple and cheap it still requires optimization due to the obtained unsatisfied yields.
